Stool samples frequently must be prepared for medical diagnostic analysis. Stool samples may be analyzed to help diagnose medical conditions ranging from parasitic, bacterial or viral infections to inflammatory bowel disease and colorectal cancer.
Colorectal cancer is a leading cause of death in Western society. However, if diagnosed early, it may be treated effectively by surgical removal of the cancerous tissue. Colorectal cancers originate in the colorectal epithelium and typically are not extensively vascularized (and therefore not invasive) during the early stages of development. Colorectal cancer is thought to result from the clonal expansion of a single mutant cell in the epithelial lining of the colon or rectum. The transition to a highly vascularized, invasive and ultimately metastatic cancer which spreads throughout the body commonly takes ten years or longer. If the cancer is detected prior to invasion, surgical removal of the cancerous tissue is an effective cure. However, colorectal cancer is often detected only upon manifestation of clinical symptoms, such as pain and black tarry stool. Generally, such symptoms are present only when the disease is well established, often after metastasis has occurred, and the prognosis for the patient is poor, even after surgical resection of the cancerous tissue. Early detection of colorectal cancer therefore is important in that detection may significantly reduce its morbidity.
Invasive diagnostic methods such as endoscopic examination allow for direct visual identification, removal, and biopsy of potentially cancerous growths such as polyps. Endoscopy is expensive, uncomfortable, inherently risky, and therefore not a practical tool for screening populations to identify those with colorectal cancer. Non-invasive analysis of stool samples for characteristics indicative of the presence of colorectal cancer or precancer is a preferred alternative for early diagnosis, but no known diagnostic method is available which reliably achieves this goal.
Current non-invasive diagnostic methods involve assaying stool samples for the presence of fecal occult blood or for elevated levels of carcinoembryonic antigen, both of which are suggestive of the presence of colorectal cancer. Additionally, recent developments in molecular biology provide methods of great potential for detecting the presence of a range of DNA mutations or alterations associated with and indicative of the presence of colorectal cancer. The presence of such mutations theoretically can be detected in DNA found in stool samples during the early stages of colorectal cancer. However, stool comprises cells and cellular debris from the patient, from microorganisms, and from food, resulting in a heterogeneous population of cells. This makes detection of a small, specific subpopulation impossible to detect reliably.
Stool diagnostic assays for colorectal cancer described in the art typically are performed on samples prepared from randomly sampled portions of voided stool. However, samples prepared according to such methods do not reproducibly yield characteristics indicative of the presence of colorectal cancer or precancer, even when prepared from stool voided by a patient with colorectal cancer or precancer. There is therefore a need in the art for methods for early diagnosis of colorectal cancer or precancer that will reproducibly detect characteristics indicative of the presence of cancerous or precancerous material in samples prepared from stool voided by a patient with colorectal cancer or precancer. Such methods are provided herein.